There are a big number of programming languages. Some of them grow up and become very popular. People use such languages more and more often. The founder of such language (or founding organisation/community) may try to implement changes to make the language better. But sometimes it's hard to make some changes because of back-comparability and such ugly things have already existed in the language for years, and are used by many users.

Are there any architectural principles or steps, during the language design phase, which can help to make it more stable so the language designers won't be as afraid to break back-comparability?